The Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional reciprocating printhead designs. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute, speeds previously unattainable with conventional inkjet printers.
The high resolution and print speeds are largely due to the self cooling operation of the printheads. Excess heat does not build up in the nozzles because it is removed from the printhead with the ejected ink drops. This allows the nozzles to be closer together and the nozzle firing rate is limited only by the ink refill rate. The self cooling operation relies on low ejection energies which in turn correspond to small nozzles and low drop volumes. Another factor that assists low energy ejection is a short nozzle aperture length. The nozzles define a geometric shape (typically circular or elliptical) and the aperture length is the thickness of the structure (such as a nozzle plate) which defines the nozzle. A long nozzle aperture length has a high fluidic drag on the ink drop as it is ejected through the nozzle. The Applicant's printhead designs keep the nozzle aperture length relatively short (less than 5 microns).
The small nozzles clog easily and paper dust or dried ink on the nozzle face (the exterior surface defining the array of nozzle apertures) can cause color mixing between closely spaced nozzles of different color. To deal with these problems, the printhead requires a sophisticated maintenance facility that can perform a variety of maintenance operations or printhead recovery techniques. The Applicant has developed a maintenance facility that moves relative to the printhead and performs different maintenance functions during the operation of the printer.
As the printhead is a pagewidth printhead, the amount of ink purged from all the nozzles during some of the maintenance functions is large. The maintenance facility can collect and hold a quantity of ink received by the various maintenance stations but if this is filled to capacity after prolonged use, ink may not drain away from the individual maintenance structures as intended. This is detrimental to the operation of the maintenance structures and can ultimately result in artifacts on the printed image.